1. Field of the Invention
The present invention relates to an oxide magnetic material used for cores of chip coils and, more particularly, an oxide magnetic material which enables to produce chip coils with low loss at high frequencies of not less than 100 MHz and small temperature coefficient of inductance (L).
2. Prior Art
Recently, with the improvement in the precision of the electronic devices and the increase in operating frequencies thereof, the requirements for characteristics electronic parts are strict recently. In particular, wound chip coils, which have been used widely in amplifier circuits and oscillation circuits of electronic devices such as image processing devices and communication devices, are required to have high Q at high frequencies of 100 MHz and above. Also, the chip coils are required to have a temperature coefficient of inductance L ranging from 0 to 750 ppm/.degree. C. since capacitors used in combination with the chip coils have a temperature coefficient of capacitance ranging from -750 to 0 ppm/.degree. C.
On the other hand, ferrite materials such as Ni-Mg-Cu-Bi ferrites have been developed as a material for magnetic cores used for high frequency chip coils, and the chip coils having a high value of Q at high frequencies have received practical application.
However, such chip coils involves some problems awaiting a solution. For example, the chip coils comprising a Ni-Mg-Cu-Bi ferrite core have the temperature coefficient of inductance (L) ranging from 1000 to 2000 ppm/.degree. C. Thus, if such a chip coil is used in combination with a capacitor of which the temperature coefficient of capacitance ranges from -750 to 0 ppm/.degree. C., the resultant circuit will have a positive temperature coefficient as a whole. Such a problem would be overcome by employing chip coils having a temperature coefficient of inductance ranging from 0 to 750 ppm/.degree. C. and capable of being used even at high frequencies of 100 MHz and above.
However, there is no ferrite material suitable for production of chip coils having a small temperature coefficient of inductance ranging from 0 to 750 ppm/.degree. C. and capable of being used even at high frequencies of 100 MHz and above.